The present invention is directed to an automatic control for refrigeration system and more particularly to a control for regulating the superheat of refrigerant in its gaseous phase existing in the suction side of the system.
Conventional refrigerator systems employ a recirculating refrigerant for removing heat from the low temperature side of the system and for discharging heat at the high temperature side. A motor driven compressor which receives low-pressure gaseous phase refrigerant and compresses it at a high pressure provides the work input necessary for the operation of the system.
The high pressure gasious phase refrigerant is supplied to a condenser where heat is removed from the refrigerant to convert it to a liquid. The liquid is then supplied through an expansion valve to the evaporator where the liquid receives heat from the cooling load, which causes the refrigerant to revert to the gaseous form. The gaseous refrigerant is then returned to the compressor for recirculation.
The amount of heat absorbed by the refrigerant in the evaporator includes the heat of vaporization of the refrigerant; that is, the amount of heat which must be absorbed by a liquid at a given temperature to convert it to a gas at the same temperatures. In addition, the gaseous refrigerant resulting from the conversion of the liquid refrigerant may absorb additional heat, which raises its temperature above the temperature of vaporization. The gaseous refrigerant in such a state is said to be superheated and the amount by which the temperature of the gas is raised above the vaporization temperature is expressed in degrees of superheat.
In many applications of refrigeration systems, such as low temperature applications, it is desired to prevent superheating of the gaseous refrigerant or to regulate the superheat of the refrigerant to a preselected magnitude. This must be accomplished by controlling the flow of liquid refrigerant into the evaporator.
In an effort to provide better control of the gaseous refrigerant superheat, devices responsive to the temperature and/or pressure of the refrigerant itself have been placed at the outlet of the evaporator to control the amount of liquid refrigerant entering the evaporator as a function of the temperature and/or pressure of the refrigerant leaving the evaporator.